As we all know, in a full-size passenger car and a sport car, a front windshield and a rear structure are provided at the front side and the rear side of a cabin respectively. The rear structure, such as a separator wall or plate, separates the cabin from the trunk of the car. A rear windshield is provided above the rear side of the rear structure. Door frames are provided at both sides of the cabin. A surrounding border of the cabin is formed by connecting the car door frames with the front windshield at the front side and connecting the car door frames with the rear structure and the rear windshield at the rear side. A fixed cabin roof cover plate is provided above the front windshield, the door frames and the rear windshield. In a compact car, a front windshield and a rear surrounding border are provided at the front side and the rear side of a cabin respectively. The door frames are provided at both sides of the cabin. A surrounding border of the cabin is formed by connecting the car door frames with the front windshield at the front side and connecting the car door frames with the rear surrounding border at the rear side. A fixed cabin roof cover plate is provided above the front windshield, the door frames and the rear surrounding border. The front and rear parts of the roof cover plate of the car cabin have substantially the same height. In comparison with a sport car, the car with a fixed cabin roof cover plate, which has substantially the same height in the front and rear, provides lower traveling speed, poor stability and high fuel consumption. To reduce the resistance and the fuel consumption, and to increase the traveling speed and improve stability, the backward slope of the cabin roof plate of a sport car is large, the rear part of the cabin roof plate is much lower than the part. The sport car with a fixed cabin roof plate, which has large backward slope and has a much lower height in the rear side than in the front side, can not provide enough space in the back seat for adult people, and only children and pets can be fitted into the back seat.